AN INVESTIGATION OF THE DIFFUSION OF SILICON IN DELTA-DOPED GALLIUM-ARSENIDE, AS DETERMINED USING HIGH-RESOLUTION SECONDARY ION MASS-SPECTROMETRY

Silicon delta-doped samples of various densities were grown by molecular-beam epitaxy and analyzed using high-resolution secondary ion mass spectrometry. A marked difference was observed between profiles produced from samples doped below a surface density of 1.3 x 10(13) cm-2, where all the silicon was incorporated on gallium sites, and highly doped samples, where autocompensation had occurred. All samples were grown at nominally 580-degrees-C and all the doped planes showed some degree of broadening. A computer model of a two-step diffusion process was developed which produced a set of diffusion coefficients for the lower-doped samples. The diffusion coefficient associated with the post deposition growth for these low-doped samples was approximately 4.2 X 10(-17) cm2 s-1. The more highly doped samples, because of their complicated profiles, were modeled using a graphical technique. This technique revealed the presence of a much larger diffusion coefficient, which is tentatively assigned to silicon diffusing as nearest-neighbor pairs.